My baby is measuring small...I'm at 35+3 & only today he's up to 4lb 14! But they're not that accurate so your LO could be bigger or smaller! You'll be fine though...I know many people who's baby's have been bigger or smaller than they say from the scans.
I don't think they generally change your due date after your 12 week/ dating scan (in the uk anyway), that is large for 30 weeks but they I know on my last growth scan it did say it can be up to 25% off either way, which is a huge amount!
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